1. Field of the Invention
This invention relates to card frames, and is more particularly directed to card guides thereof.
2. Description of the prior art
A `card frame` (also known as a `sub-rack`) is a kind of frame structure used to house electrical circuitry mounted on `cards` which, for example, comprise circuit boards, for instance printed circuit boards, mounting circuit components. A typical card frame comprises a pair of side plates spaced apart by generally horizontally extending cross rails. Card guides are mounted on at least some of the cross rails to receive the cards, each card guide generally comprising an elongate member extending between a front and a rear cross-rail and having a channel to receive a portion of the card, e.g. an edge of a circuit board, as the card is slid into the card frame. Clearly, once mounted in place on upper and lower sets of front and rear cross-rails, an associated pair of upper and lower card guides can receive only a card of a predetermined height. Thus, only cards of that particular height can be received between the two sets of cross rails. This is acceptable if all of the cards to be fitted between those two sets of cross rails are of the same height; for instance if they are standard height `Eurocards`. Sometimes, however, there may be a requirement to use cards of other heights instead of or even in conjunction with standard height cards such as Eurocards. This presents the manufacturers of card frames and the components thereof with something of a problem since they endeavour to provide a more or less standard range of products which can be supplied to electronics manufacturers for mounting their cards. Thus, if a particular card frame is designed to accept, say, Eurocards, if a particular user wishes to use cards of a different height instead of or even in conjunction with Eurocards, a technically unsatisfactory compromise often is required. For instance, if cards of a different height are to be used, this could be accommodated by moving the associated upper or lower cross rails. This would usually require an additional complication such as the provision of additional fixing apertures and location means on the side plates. If cards of different heights are to be used together between the same sets of cross rails, the cross rails must be positioned for the card of greater height and the card guides for the card of lesser height will have to be spaced from the cross rails by special spacer means.